1. Field of the Invention
The present invention relates generally to an NB-TDD (Narrow-Band Time Division Duplexing) system, and in particular, to a method and apparatus for sharing a DL-DPCH (Downlink Dedicated Physical Channel).
2. Description of the Related Art
Subscribers to wireless communication networks, such as cellular, PCS (Personal Communications Services), and IMT-2000 (International Mobile Telecommunication-2000) communication systems, can connect to the Internet in any environment by using Internet-enabled mobile terminals or by connecting laptop computers to an existing mobile communication network, e.g., through software/hardware MODEMs.
UMTS (Universal Mobile Telecommunications System) or WCDMA (Wideband Code Division Multiple Access), a 3rd generation communication system, is developed to work with a packet switching system such as GPRS (General Packet Radio Services) using CDMA (Code Division Multiple Access). The UMTS system supports high-speed packet data service as well as voice service, and enables high-speed transmission of data and moving pictures. Commonly, a radio network in the UMTS communication system is called a UTRAN (UMTS Radio Access Network), or more simply a RAN. The RAN includes Node Bs, which are equivalent to base stations, and RNCs (Radio Network Controllers), which are equivalent to base station controllers (BSCs).
NB-TDD is one of the 3rd generation standards for physical interfacing between a Node B and a UE (User Equipment) in the WCDMA communication system.
FIG. 1 illustrates a conventional NB-TDD physical channel configuration. Referring to FIG. 1, an NB-TDD physical channel can be divided into radio frames 101, each being 10 ms in duration. Each radio frame 101 is further divisible into two subframes 102. Each subframe 102 includes a DwPCH (Downlink Pilot Channel) 103, a guard period (GP) 104, an UpPCH (Uplink Pilot Channel) 105, and 7 time slots (TSs) 106 (TS #0-TS #6) for delivering data.
Each TS 106 can be divided into 4 parts: a 352-chip first data area 107, a 144-chip midamble 108, a 352-chip second data area 109, and a 16-chip GP 110.
However, the above-described TS structure is a mere example. Therefore, the TS format varies with the configuration of an actual channel.
For example, in FIG. 1, a TFCI (Transport Format Combination Indicator) is separated into two parts 111 and 112. The TFCIs 111 and 112 are positioned before the first and second data areas 107 and 109, respectively. As another example, synchronization information, an SS (Synchronization Shift) 113 and a TPC (Transmit Power Control) 114 may further be included.
The TFCIs 111 and 112 indicate how transport channels at a higher layer than physical channels are mapped to the physical channels. The SS 113 is used by a UE to synchronize to a Node B for uplink transmission. The TPC 114 is used to control transmit power. Each radio frame is code-divided by 16 codes.
Two time slots at the same position in two subframes of each radio frame form one channel. For example, the second TS in the first subframe and the second TS in the second subframe are used as a DPCH for a specific UE. The DPCH delivers a control parameter from the Node B to the UE, which is essential in determining the structure of an enhanced uplink on which the UE transmits data at high rate to the Node B.
However, the control parameter is rather small in size. Therefore, it may not always need to occupy two TSs, that is, one DPCH fully. In this case, the dedicated use of the DPCH for one UE unnecessarily dissipates all the system resources.